In a projector of a DLP (digital light processing; a registered trademark of Texas Instruments Incorporated of the United States) system, image projection is performed with an optical semiconductor called a DLP chip containing millions of small mirrors (micromirrors). In the case of a three-chip DLP system that uses three DLP chips, lamp light is separated into the three primary colors of RGB with a specially designed prism, and each DLP chip is illuminated to display a color image. In the case of a one-chip DLP system that uses one DLP chip, on the other hand, lamp light is separated into the three primary colors of RGB with one color wheel colored in the three colors of RGB, and the one DLP chip is illuminated to display a color image. The color wheel rotates at high speed, and accordingly, the micromirrors are switched on and off at high speed. Therefore, the image appears to be an RGB combined color image to the human eye, due to an afterimage effect.
Digital micromirror devices such as the above mentioned DLP chips are already common as reflective image display elements for projectors. A digital micromirror device has an image display surface that is formed with a plurality of minute micromirrors, and controls the tilt of each mirror surface on the image display surface to perform intensity modulation on illumination light so that an image is formed. That is, switching on and off of each pixel of the digital micromirror device is performed by rotating the mirror surface ±12 degrees about the rotation axis at an angle of 45 degrees with respect to each side of the image display surface (in other words, micromirror drive being performed about one axis). As for movement of the micromirrors, Non Patent Literature 1 discloses a digital micromirror device of a new operation type (Tilt & Roll Pixel DMD) that performs micromirror drive about two orthogonal axes.
Various types of projectors have been suggested (see Patent Literatures 1 through 3, for example) as projectors equipped with reflective image display elements such as the above described digital micromirror device, and there is a demand for projectors that are bright (with small F-numbers), have high contrast, and have high image quality.